Speech intercommunication system between remote points



KILMINSTER -BETWEEN REMOTE POINTS Filed Sept. 7, ,1948

SPEECH INTERCOMMUNICATION SYSTEM REQ May 29, 1951 I N VEN TOR. Wwf/@ymmny KVM/hte@ Patented Vay 29, 1195i SPEECH INTERCOMMUNICATION SYSTEMBETWEEN' REMOTE POINTS Shirley Anthony Kilminster, Smethwick, Eng-1and'assignor to Vernon Joseph Hadley and Norman Cecil Hadley, both ofSmethwick, Eng.-

land

Application September 7, 1948, Serial No. 48,028 In Great BritainFebruary; 23,. 194.8

4 Claims. (Cl. 179-37) This invention hasreference to improvements inspeech intercommunication systems between remote points, of the kindwherein each remote point is provided with a loud speaker device adaptedfor two-way speech. Such systems are known wherein a main unit canprovide twoway speech communication with any one of a plurality-ofsubsidiary unitsV at the will of the operator of the main unit.

I The object of the present invention is to provide agsystem oftheaforesaid kind wherein any unitv may be pui'l intctwo-wayspeechfcommunication with any other unit, means being provided forensuring that no interference from a third unit can obtain whileintercommunication is taking place.

The invention consists-in` aV speech intercommunicationsysterrigbetween` remote points of the kind referredtowherein each pointis provided with a unitl comprising a loud. speaker and a switchassociatedgwith a circuit to each other unit of the systemvremotetherefrom; the operationy of one of' said'` switches closing acircuit through a pair of relayswhich close the circuit to the.requiredv remote unit and atthe same time opencontactsa to isolate; theremaining units of the system.

The invention will nQWbe described with reference to the accgmpanyingwiringdiagram which forthe sake of clarity. embodiesonly vsufricient ofthe circuit forga understanding of the invention and in Whicho 1y.; twounitsA designated One and Two are shown., Eachunitl embodies a loudspeaker; L and"M ai series ofv switches corresponding in number to;the;` number of other units in the system.A F91' example, Unit One hasswitches S2 S3, S4, etc.; UnitL Two has switches SI, S3, S4, etc.; theother unitsbeng similarly arranged. Each switch*` SI, S2, S3, is capableof closing a; circuit through a pair of associated relays;` RIXI, RZXZ,and R3X3, through therespective-contactsgXIA, X2A, XSA and'XI B, or XZBor-XSB, These relays and contacts and those-V hereinafterreferred to,are housed within acasing; which also'incorporates an amplier A,anfoscillatorvalve-.V anda suppressor circuits, connectedas shownin thediagram to a suitable-source ofhighstension voltage; supply. Thefoscllatorfvalve V normally cannot.operate-sincethecathode thereof ismaintained atl ahgh positive; potential by virtue., of the resistances.-Yjand; Z., When however the low resistancer of "ai, speaker isiconnected across the resistance Y as will hereinafterfbe:moreiullydescribed.. the highzpnsitiye. pteutial. at the cathode is removed andthe valve oscillates emitting a calling tone from the appropriatespeaker whilst emitting a faint calling tone in the speaker of thecalling unit due to induction in the wiring. Each unit has a furtherswitch M provided with ofi (contact b closed) listen (contact a closed)and talk (contacts a and c closed) positions whereby two-way speech canbe obtained. The switch M is associated with a relay RM` operatingcontacts RMA whereby the loud speaker of a unit may bev connected to theinput or output side of the amplifier A.

Operation In operation assumingV that the remote Unit One wishes to.call the remote Unit Two, the switch S2 at the Unit Oneis closed thusclosing a circuit from B+ through the relay R2, switch S2, relay Xi andcontact XIB to ground. The energisation of the relay R2 closes thecontacts RZB and REA, whilst the energisation of the relay XI closes thecontacts XIC and XID and changes the contacts XIB from the positionshown in the diagram to the alternative normally open position so as toby-pass the contact XIAwhich is` alsdopenedby the relay XI. The openingof the A contact of the X relay shorts asimilar circuit for any otherremote station preventing.r interruption ofthe circuit in use unless thesystem is clear but,y through the bypassj holds the relays R andy X ofthe called and calling stations, respectively, in circuit. The Bcontacts of the relays X are so arranged that the normally open contactof the pair closes before the normally closed contact opens, thuseliminating uttering.

Closure offcontact RZB' establishes a circuit for a calling tone to theloud speaker in the remote Unit Two from theoscillator valve V, thecathode of whichisconnected to the loud speaker throughcontact RZB andthe contact b of switch M2vr thereby removing the high positivepotential whichnormally obtains at the cathode of the valve V. Thecalling tone is heard in vUnit Two. Sinti-ultaneously,l the relay XI hasclosed contact XIC connnecting` the output side of the amplier tocontacta of the switch MI in Unit One. The person calling from Unit Onehas already moved switch MI to the listen position, closing contactsfcand thus the amplifier output is connected rto the speaker of Unit One.Due to inductance and capacity between the wires of the multi-lead cableleading to Unit One, theoscillator call tone is also picked up in thespeaker of Unit One as an indication to the opn erator there that hiscall is being made.

If the system were in use by two other stations, Unit One would not beable to establish its original circuit through the series contacts A ofthe relays XI---Xn and the lack of a call tone in its own speaker wouldindicate that the system was busy.

The energization of the relay R2 also has closed its contact RZA whichconnects the input side of the amplier through contacts RMA to the acontacts of the switch M2 in Unit Two.

Assuming that the call has come through, and that the operator at UnitTwo wishes to answer, he does so by moving the switch M2 to talkposition, closing contacts a and c and opening contact b which restoresthe high positive po tential at the cathode of the valve V cutting outthe calling tone and at the same time connecting Unit Two loud speakerwith the input side of the amplifier A through contact a and relaycontacts RZA and RMA.

After the operator at Unit Two has replied, further control of theconversation remains in Unit One. When he wishes to talk, he movesswitch MI and talk position, closing its contacts a and c and openingits contact b. The closure of contact c establishes a circuit from B+through relay RM, contact XID, contact c or" switch MI, relay XI, andthe now closed contact of contacts XIB to ground. This causes relay RMto shift its contacts RMA, reversing the connections of the amplierinput and output.

It will be appreciated that all units can be identical and by increasingthe number of relays in the casing the number of remote units in asystem can be increased, but desirably one unit of the system (in thediagram unit I) is provided with a priority switch P. It will be notedthat, although under normal operating conditions the contacts B` of therelays XI, X2, X3, etc., are all similarly connected, yet the normallyopen contacts of these pairs for relays X2, X3, etc., are all connectedin parallel to a by-pass lead around the series of A contacts for relaysX2, X3, etc., whereas the normally open side of contacts XIB isconnected to a by-pass which also leads around contact XIA. Thus anoperator at Unit One, who has priority, can establish a circuit to anyother station regardless of the call which may be in progress byinterrupting the communication between the two other units by theopening of contact XIA.

If an operator at any station other than Unit One wishing to make a calliinds the system busy, he cannot interrupt but can, by leaving theappropriate switch S closed, condition the system to make his call assoon as the two talk ing stations have restored the system by movingtheir switches M to off position.

Although the drawings and the above description show only two stations,viz., Unit One and Unit Two, provision is made for connecting Unit Threeto relays and contacts shown in the drawings and other units such asFour, Five, etc., can be installed in the system merely by duplicatingthe relays and connections which are already shown for Units One andTwo.

I claim:

1. In an intercommunication system, in combination, a plurality ofseparated stations each including a speaker, a station selector switchand a control switch, said station selector switch having a commonterminal and a terminal for each station to be called, a central controlincluding an amplier, a called station relay corresponding to eachstation, a calling station relay for each station, an amplier controlrelay, a source of current, said called station relays each having anoperating coil that is connected between the source of current and theseveral station selector switch terminals corresponding to thatparticular called station, each calling station relay having anoperating coil that is connected to the common terminal of thecorresponding stations selector switch and to the return side of thesource of current, a signal lead from each operators station, an inputand an output line to the amplifler, said control relay having reversingcontacts connected in the input and output lines, contacts on eachcalling station relay and called station relay that serve to connect thesignal leads of the called and calling stations to the input and outputlines of the amplier and a circuit from the calling station controlswitch through said control relay for conditioning the control relay fortalking or listening at the calling station.

2. In an intercommunication system, in combination, a plurality ofseparated stations, a speaker at each station, a selector switch and acontrol switch at each station, said selector switch having a commonterminal and a terminal for each station to be called, a signal leadfrom each of the separated stations, an amplifier including a source ofcontrol current, a called station relay for each separated station, saidrelays each having an operating coil one terminal of which is connectedto the source of current and the other of which is connected to thecorresponding terminal of the several selector switches, each calledstation relay having at least one set of normally open contacts oneterminal of which is connected to the signal lead of the correspondingstation, an input and an output lead for the ampliiier, a control relayhaving reversing contacts in said input and output leads, said calledstations relays each having the other of its contact terminals connectedto one of the amplifier leads, a calling station relay for each separatestation, each calling station relay having an operating coil oneterminal of which is connected to the common terminal of thecorresponding selector switch, a plurality of sets of contacts on `eachcalling station relay, each of said calling station relays having theother terminal of its operating, coil connected to the return side ofthe current source through a circuit including a normally closed set ofcontacts on that relay and a series circuit including one of thenormally closed set of contacts of each calling station relay, and acircuit from each calling station relay coil that includes one of thenormally open sets of contacts of that relay and that is in parallelwith at least some of the series connected normally closed contacts, andan operating circuit for said control relay that includes the controlswitch of the calling station and a set of normally open contacts of thecorresponding calling station relay, whereby operation of the selectorswitch at a calling station energizes the calling relay for that stationand the called relay for the called station, connects the'signal leadsof those stations to the amplier, connects the control relay to thecalling station control switch for controlling Y.

the direction of transmission through the system, and opens the callingcircuits for the other separated stations.

3. In an intercommunication system according station relay through thecontrol switch to the current return, which circuit serves to conditionthat station for use in preference to other stations.

SHIRLEY ANTHONY KILMINSTER.

REFERENCES CITED The following references are of record in th le of thispatent:

UNITED STATES PATENTS Number Name Date 2,162,370 Campbell June 13, 19392,249,456 Campbell July 15, 1941 2,255,517 Nickerson et al. Sept. 9,1941 2,269,144 Campbell Jan. 6, 1942 2,347,079 Campbell Apr. 18, 1944L

